Field of Invention
This invention relates to tyre in tyre systems in which a wheel is provided with an outer ground engaging tyre mounted on a rim of the wheel and an inner inflatable member is mounted on the rim inside the outer tyre, the wheel rim having a first inflation valve mounted on the rim to introduce air into and release air from the inner inflatable member, and a second inflation valve mounted on the rim for introducing air into and releasing air from the interior of the ground engaging tyre external to the inner inflatable member.
Description of Related Art
Such tyre in tyre systems are well known (see, for example, U.S. Pat. No. 7,219,540 and the present applicants European patent EP-B-2605922) as a convenient arrangement to allow the tyre pressures of large tyres, such as those used on agricultural tractors, to be relatively easily changed between the relatively low pressures of say 0.8 bar used when undertaking field work to the higher pressures of say 2 bar used on road work. These systems speed up the changing of the effective tyre pressure as often only the pressure of the volume external to the inner inflatable member needs to be changed to achieve the required effective tyre pressure. This significantly reduces the volume of air which must be pumped in or vented.
The ability to relatively easily and speedily change between field and road pressures is becoming increasingly important as it is necessary to operate the tractor as economically and safely as possible which requires the use of the appropriate tyre pressure at all times. Care must be taken to avoid contact between the inner inflatable member and the outer tyre which can result in abrasion and damage to both and is a particular risk when operating at relatively low pressures during field work.
It is an object of the present invention to provide a wheel with a tyre in tyre system which addresses at least some of the above issues.